1. Technical Field
The present invention relates to freestanding III-nitride single-crystal substrates that are of low average dislocation density and are fracture resistant, and to methods of manufacturing semiconductor devices utilizing the substrates.
2. Description of the Related Art
III-nitride single-crystal substrates whose dislocation-density distribution is uniform and whose average dislocation density is low are being developed as freestanding III-nitride single-crystal substrates ideally suited to application in semiconductor devices including light-emitting devices and electronic devices.
In Japanese Unexamined Pat. App. Pub. No. 2004-193371 (Patent Document 1), for example, a freestanding substrate incorporating a III-nitride semiconductor layer of less than 1×106 cm−2 average dislocation density is disclosed—specifically, a GaN film (freestanding substrate) in which the dislocation density varies within a 0.12 to 1.5×106 cm−2 range. In Japanese Unexamined Pat. App. Pub. No. 2006-52102 (Patent Document 2), meanwhile, a III-V Group nitride system semiconductor substrate whose average dislocation density is 5×107 cm−2 or less is disclosed—specifically a GaN freestanding substrate having a dislocation-density range of 1.4±0.7×106 cm−2.
Nonetheless, freestanding III-nitride single-crystal substrates of still lower dislocation density are being sought as substrates for semiconductor devices, in order to improve semiconductor device properties further.    Patent Document 1: Japanese Unexamined Pat. App. Pub. No. 2004-193371    Patent Document 2: Japanese Unexamined Pat. App. Pub. No. 2006-52102
Accordingly, the manufacture of freestanding III-nitride single-crystal substrates of still lower dislocation density—for example, of 5×105 cm−2 average dislocation density—has been attempted. With, at an average dislocation density of 5×105 cm−2, ultra-low density freestanding III-nitride single-crystal substrates, however, those whose dislocation-density distribution is uniform have been discovered to be fracture-prone.